Parallax computation apparatus



Jan. 5, 1960 c. w. MILLER 2,919,849

PARALLAX COMPUTATION APPARATUS Filed Feb. 3, 1949 4 Sheets-Sheet 2 Phcos E'b fia -Ph CATHOD E SERVO FOLLOWER AMPLIFIER INVENTOR CARLTON W.MILLER ATTORNEY Jan. 5, 1960 c. w. MILLER PARALLAX COMPUTATION APPARATUS4 Sheets-Sheet 4 Filed Feb. 3, 1949 I INVENTOR CARLTON m MILLER BY X9(9m ATTORNEY United States Patent PARALLAX COMPUTATION APPARATUS CarltonW. Miller, Rochester, N.Y., assignor, by mesne assignments, to theUnited States of America as represented by the Secretary of the NavyApplication February 3, 1949, Serial No. 74,442-

'5 Claims. (Cl. 23561) This invention relates to a parallax computationapparatus, and more particularly an apparatus employing electrical servosystems for rapidly and simply computing a unit horizontal parallaxcorrection suitable for making horizontal parallax corrections to thetrain orders of a gun or a number of guns located at different points ona vessel and firing at the same target.

In gun fire control, the director is usually located at a distance of atleast several yards from the gun; such an arrangement necessitates ahorizontal parallax correction to take account of the horizontalcomponent of the angle between the line from target to director, and theline from target to gun.

An accurate solution of the parallax problem would have to be based onthe future position of a moving target. In the instant invention, thepresent or instant position of the target is utilized for parallaxcomputation, and the computed parallax correction multiplied by aconstant 9/8, to take account of the fact that the most dangeroustargets are those moving toward the vessel.

The solution of the parallax problem involves solving the followingequation:

B sin Brp Ph. cos Eb T Ic1 4 in which the terms employed may be definedas follows:

B'rp-Director train corrected for horizontal parallax to the referencepoint of the ship which is assumed to be 100 yards aft from the gun.

B'r'-Director train (sight non-stabilized). The angle between thefore-and-aft axis of own ship and the line of sight to the targetvertically projected into the deck plane, measured clockwise from thebow of own ship.

E'bDirector elevation. The elevation of the director line of sight tothe target above the deck, measured in a plane perpendicular to thedeck.

R-Range. The distance in yards from the director to. the target(measured along the line of sight).

R Projected range. The vertical projection of R into the deck plane.

Ph-Horizontal parallax. The angular correction to be applied to guntrain order for a gun which is 100 yards fore of the reference point.

ePh--Error signal of the parallax angle.

Pbh-Horizontal parallax base length to reference point of ship. Theprojection into the deck plane of the distance measured in yards betweenthe director and a selected reference point of the ship on thefore-andaft axis of the ship, positive when the director is aft of thereference point.

Pbh and hence Ph will vary as the parallax solution is obtained fordifferent gun positions.

The parallax computation apparatus of the instant invention isparticularly well adapted for use with the invention described andclaimed in the application of Ivan A. Getting for Gun Fire ControlMethod and System, Serial No. 61,558, filed November 23, 1948.

2,919,849 Patented Jan. 5, 1960 An object of the instant invention is toprovide new and improved horizontal parallax computation apparatusemploying a minimum number of servo systems.

Another object is to provide new and improved horizontal parallaxcomputation apparatus characterized by simplicity and a high degree ofaccuracy.

A further object is to provide new and improved apparatus for computinga unit horizontal parallax correction which may be appliedsimultaneously to a number of guns positioned at different distancesfrom the director or reference point.

Still a further object is to provide horizontal parallax computationapparatus in which the speed of computation is regulated to besubstantially uniform over a wide range of parallax values.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description, when considered inconnection with the accompanying drawings wherein:

Figs. 1A, 1B and 1C taken together comprise a schematic circuit diagramof a complete electrical system and apparatus suitable for practicingthe method of the in vention;

Fig. 2 is a simplified schematic diagram of the apparatus of Figs. 1A,1B and 1C; and

Fig. 3 is a diagram illustrating the geometry of the parallaxcomputation problem vertically projected into the horizontal planeincluding the gun, that is, the deck plane.

In Figure 3 the symbols used have the following meanmgs:

B'rThe horizontal director train angle.

BThe displacement of the director from the gun.

D-The director position.

R The projection of target range, R, into the horizontal plane.

T The projection of the target in the horizontal plane.

LA line perpendicular to the line GT Ph-The horizontal parallax angle.

Referring now to the drawings in which like reference numerals are usedthroughout to designate like parts, and in particular to Figs. 1A, 1Band 1C thereof, an Eb servo motor 26 positions the shaft of a synchrogenerator 16, to which v., A.C., 60 cycles is applied from a suitablesource, not shown. The resistance network comprising resistors 31, 32and 33 is connected across the three terminals of generator 16 toprovide proper loading and to insure that the voltage developed acrossleads 54 and 55 is substantially proportional to the quantity cos Eb,generator 16 being suitably constructed for this purpose. Resistors 31and 32 may have a value of 2 kilohms each and resistor 33 a value of 3.3kilohms.

The voltage developed across leads 54 and 55 is applied by way ofalignment potentiometer 34 to the terminals of a tapped potentiometer19, the arm of which is positioned by the quantity Ph by suitablemechanical connection 50 to a Ph servo motor 13. Potentiometer 19 mayhave a value of 5 kilohms. Lead 56 is connected to the tap onpotentiometer 19, and lead 57 is connected to the arm of potentiometer19. The voltage appearing across leads 56 and 57 is proportional to Phcos E'b it being understood that the constant k14, which may have avalue of 9/8, may be introduced by suitable proportioning of the circuitconstants.

The constant kl4 is necessitated by the fact that whereas the parallaxcorrection should preferably be made for the future position of thetarget, in the instant system the correction is made for present orinstant position, this being a simpler method of computation. Since themost dangerous targets are those which are moving toward the director, aconstant is introduced to make the parallax angle larger. Byexperimentation, the value 9/8 has been found suitable for this purpose.

A Brp servo motor 15, by suitable mechanical cou pling to a generator18, positions the shaft thereof. Generator 18 is energized by 110 v.,A.C., 60 cycles and has three output terminals across which is connectedthe resistance network comprising the resistors 41, 42 and 43 to providecorrect loading for the generator. Generator 18 is constructed andarranged so that the voltage developed therefrom across leads 56 and 71is proportional to the quantity sin B'r'p.

Lead 71 is connected to the arm of a potentiometer 17 which may have avalue of 100 kilohms, and which has the arm thereof positioned by thequantity R by suitable mechanical coupling to an R servo motor 30. Oneend of potentiometer 17 is connected by way of resistor 27, which mayhave a value of 3360 ohms, to lead 56, while the other end ofpotentiometer 17 is connected by way of resistor 28, which may have avalue of 1748 ohms, and resistor 29, which may have a value of 1611ohms, to lead 56.

The junction between resistors 28 and 29 is connected to one terminal ofa secant attenuator 14 which may have a total value of 20 kilohms, theother terminal of the attenuator 14 being connected to lead 57.

The arm of attenuator 14 is positioned by the quantity of E'b bysuitable mechanical coupling to an E'b servo motor 26, and the arm isconnected by way of lead 45 to one input terminal of a filter 23, theother input terminal of filter 23 being connected by way of lead 44 tothe junction between resistors 28 and 29.

The output of filter 23, which may be of conventional design, isdelivered by leads 21 and 22 to a cathode follower 24, the output ofwhich is applied to a servo amplifier 25 which in turn drives the Phservo motor 13.

Motor 13 is operatively connected by aforementioned coupling 50 to anA.-C. tachometer 39, the tachometer being connected by way of lead 44,and lead 46 and resistor 38, which may have a value of 62 kilohms, tothe input of filter 23, for providing a stabilizing voltage therefor.The tachometer 39, may, if desired, be a D.-C. tachometer, and means,not shown, provided for converting its output to A.C. before mixing withthe error signal at 23.

Dial 47 indicates the value of the quantity of Ph. Coupling 50 also hasconnected thereto a Ph generator 20 suitably energized from a source of110 v., A.C., 60 cycles, not shown, and is provided for giving a Phoutput signal for transmission to gun and fuze servos.

A B'r' drive or servo motor 35 is operatively connected to a pair ofservo generators 36 and 37, which are both suitably energized from asource, not shown, of A.C. potential of 110 v., 60 cycles. Connectedacross these generators 36 and 37 are capacitance networks 74 and 73respectively, for increasing the power factors of the circuits. Theoutput of generator 36 is applied to a differential generator 11, andthe output of generator 37 is applied to a differential generator 11'.The shafts of both these differential generators are positioned throughchange gears 12 and coupling 50 from the Ph servo 13, and their outputsare proportional to the quantity B'r'p.

The output of the differential generator 11 is applied by way of leads51, 52 and 53 to control transformer 59, while the output of generator11' is applied by way of leads 71, 72 and 73 to control transformer 60.Transformer elements 59 and 60 have the shafts thereof positioned by thequantity B'r'p by suitable coupling 49 to the aforementioned B'rp servomotor 15. The voltage outputs of transformers 59 and 60 represent theinstantaneous error in B'r'p.

Relay 70 is provided for purposes to be hereafter apparent; whenunenergized, a circuit, by way of lead 67 and by way of lead 75, fromcontrol transformer 60 to filter 64, is completed. The output of filter64 is applied to cathode follower 65, and the output thereof is appliedto servo amplifier 66 which in turn controls servo motor 15. Motor 15 isconnected to a suitable source of A.C. potential, not shown, of theorder of 110 v., 60 cycles.

Control transformer 59 has connected in series with the output thereofthe secondary of a transformer 61 which has the primary thereofenergized from a suitable source of A.C. potential, not shown, of theorder of 110 v., 60 cycles. The secondary voltage which may be of theorder of 3 volts is of a polarity to oppose the voltage output oftransformer 59. When the voltage from 59 is sufiicient to override thevoltage from the secondary of 61, it is rectified at 62, amplified at63, and energizes the winding 68 of relay 70, thereby providing acircuit in which the voltage diiferential between 59 and 61 is appliedto filter 64.

The operation of the above traced circuit will be readily apparent tothose skilled in the art and, therefore, need not be described indetail.

Any change in the quantities Eb, B'rp, or R results in an unbalancebetween the sin B'r'p R signal applied to attenuator 14, and an ePhsignal appears between leads 44 and 45. This ePh signal drives servomotor 13, and shaft 50 operatively connected to motor 13 moves the armof potentiometer 19 in the proper direction selectively in accordancewith the polarity of the ePh signal until the signals at attenuator 14are balanced.

Fig. 2 is a simplified schematic of the circuit and system of Figs. 1A,1B and 1C, and need not be traced in detail. The designations of thevarious elements of Fig. 2 are the same as the corresponding elements ofFigs. lA-lC but are shown in somewhat more schematic form to facilitatea ready understanding of the circuit operation, which is substantiallythe same as the operation of the circuit and system of Figs. 1A-1C.

The parallax equation employed in the instant invention may be derivedas follows from Fig. 3. Gun and director are located at points G and Drespectively and separated by a distance B which may be assumed, forease in explanation, to be yards. The vertical projection of the targetT into the horizontal plane is T The target T may be thought of as beinga point directly above T if the drawing is on a horizontal surface. Thehorizontal parallax angle Ph is measured between the line from T to thegun and the line from T to director. The train angle Br is measured atpoint D, the director, between the lines DG and D--T The line L isdropped from G perpendicular to the line GT and intersecting line DT atX.

Since the angle Ph is small and since the distance DX is also small, wecan assume sin Ph Ph-- We can also assume with negligible error thatangle DXG is a right angle and therefore that sin B r Then,

B sin Br Ph R the vertical projection of range into the horizontalplane=R cos E72, where E'b is the elevation angle of the target T aboveT as is viewed from D, and R is the actual measurable range to thetarget T from D.

Therefore,

B sin B r R cos Eb Multiplying both sides by cos Eb and introducing aconstant kl4 to account for anticipated motion of the target gives:

(cos Eb) Ph B sin B r 7014 R Brp, as has been stated, is the directortrain corrected for horizontal parallax to a predetermined referencepoint of the ship and may be conveniently substituted for Br'. The lastmentioned equation then becomes:

(cos Eb) Ph B sin Brp kl4 R Accordingly, as stated before BsinB'rp Phcos Eb If B is taken as the unit of measure for R the equation becomessin Brp cos E b Before the solution of the last named equation takesplace in the aforedescribed circuit, that is, before the error signal isreduced to zero, a voltage proportional to the parallax error, ePh,times cos Eb exists in the circuit. This gives for an unbalancedcondition of the circuit the equation For a given error in Ph, theamount of this voltage depends on the value of cos Eb. As a result ofthis condition of operation the servo loop gain varies with Eb, andspeed of response and stability might become unsatisfactory at extremevalues of cos Eb. For this reason, the voltage is multiplied by sec Eb.It is to be noted that this multiplication does not materially affectthe equation solved, but regulates the gain of the servo loop. This canbe seen from a consideration that the secant of an angle variesinversely as the cosine, therefore, the cos Eb multiplied by the sec Ebyields a constant.

If, therefore, the term ePh cos Eb is multiplied by the sec Eb thevariable angle function cos Eb cancels.

It is obvious that, if desired, the parallax angle might also becomputed from a center or reference point on the vessel.

Since the unit parallax correction for a 100 yard base length isdesignated Ph, for the quantities into which the parallax correctionsenter,

cos Eb:

Pbh I I I I B r p-B 1' Ph where Pbh is the distance from the director tothe center point of the ship (positive if the director is aft of thecenter point). It is again to be noted that the factor Pbh only correctsthe director train angle for parallax to the reference point of theship.

As will be readily understood by those skilled in the art, the ratio ofchange gears 12 of Figs. 2 and 1B depends upon the distance between thedirector and the reference point.

Whereas certain values have been stated as suitable for the resistorelements employed in the circuit, it is understood that other valuescould be employed if desired.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States of America is:

1. In a ship, parallax computation apparatus for a gun and a directormovable in elevation and train having a common reference point, saidgun, director and said point being located in the same substantiallyhorizontal deck plane of the ship, and having a target, comprising incombination, a synchro generator having the shaft thereof positioned inaccordance with the angle of elevation of the target above the planeviewed from the director, Eb, said synchro generator being constructedand arranged to provide an output signal corresponding to the quantitywhich is the cosine function of the elevation angle, cos Eb, when saidshaft is positioned, first adjustable potentiometer means operativelyconnected to said generator and having the cos Eb signal appliedthereacross, the arm of said first potentiometer means being adapted tobe set to a position in accordance with the parallax angle, which is theprojection in the horizontal plane of the angle subtended at the targetby the gun and the director, Ph, said first potentiometer means beingconstructed and arranged to provide an output signal corresponding tothe quantity which is the product of the parallax angle and the cosinefunction of the angle of elevation divided by an empirical constant Phcos Eb when said arm is positioned, generator means having the shaftthereof positioned in accordance with the angle subtended at thedirector by the gun and the perpendicular projection of said target inthe horizontal plane corrected for parallax to a reference point of theship, Brp, and constructed and arranged to provide an output signalcorresponding to the quantity which is the sine function of the parallaxcorrected angle of train, sin Brp, when the shaft thereof is positioned,second adjustable potentiometer means connected to said generator means,the arm of said second potentiometer means being positioned inaccordance with the quantity R, which is the range to the target, saidsecond potentiometer means being constructed and arranged to provide anoutput signal corresponding to the quantity sin B'r'p R which is thesine function of the corrected angle of train divided by the range, whenthe arm thereof is positioned, secant attenuator means having a movablecontact element therefor and operatively connected to said first andsecond potentiometer means and having said Sin Br'p R and Ph cos Ebsignals applied thereto in mutual opposition, means operativelyconnected to said secant attenuator means for positioning said movablecontact in accordance with the angle of elevation, Eb, said secantattenuator means providing an output signal, ePh, servo motor meanscontrolled by said last output signal for providing a setting of theshaft thereof corresponding to the quantity Ph, said last named shaftbeing operatively connected to the arm ofsaid first potentiometer meansfor setting the arm to said Ph position, whereby said Ph cos E'b signalsare continually maintained in substantial equality.

2. A parallax computer having input terminals for receiving voltagesproportional to the elevation angle of a target, a train angle of adirector and the target range, said computer having an output element,said computer including means receiving said train angle voltage andconnected to receive a signal proportional to the computer output fromsaid output element to produce a modified train angle signalproportional to the sum of the inputs, means receiving said modifiedtrain angle signal producing a sine function signal proportional to thesine of said modified angle, means receiving said sine function signaland a function signal of said range to produce a quotient of said sinefunction and said range; means receiving said elevation angle voltage toproduce a cosine signal proportional to the cosine function of saidelevation angle, means receiving a portion of the computer output andsaid cosine function to produce a voltage proportional to a product ofsaid output and said cosine function, means receiving said productvoltage and said quotient voltage to compare them and to produce avoltage proportional to their difference, said output element receivingsaid difference voltage to produce a parallax angle output for computer,said output means being operative to drive said means for producing saidproduct voltage to reduce said difference voltage to zero.

3. In a ships horizontal parallax computation apparatus for a gun and adirector movable in elevation and train and having a common referencepoint, said gun, director and said point being located in the samesubstantially horizontal deck plane of the ship, and having a target, incombination, first means for obtaining a signal proportional to thequantity which is the cosine function of the angle of elevation of thetarget above the plane viewed from the director, cos Eb, second meansoperatively connected to said first named means for obtaining from saidsignal a second signal proportional to the quantity which is the productof the vertical projection in the horizontal plane of the anglesubtended at the target by the gun and director and the cosine functionof the angle of elevation divided by a constant Ph cos E1) where kl4 isa constant, third means for obtaining a third signal proportional to thequantity which is the sine function of the angle subtended at thedirector by the gun and the perpendicular projection of said target inthe horizontal plane divided by the range to the target a secant signalvoltage attenuator means having said and sin B'r'p R and Ph cos Ebsignals applied thereto in mutual opposition so as to provide a voltageproportional to their difference, said attenuator means providing afractional part of said difference as an output, fifth means foradjusting said fractional output according to the secant of the angle ofelevation of the target, said angle being E'b, servo motor meansresponsive to the output of said attenuator for producing rotationcorresponding to the projection in the horizontal plane of the anglesubtended at the target by the gun and director, said servo motor meansbeing operatively connected to said second means receiving the output ofsaid servo means.

4. In a ships horizontal parallax computation apparatus for a gun and adirector movable in elevation and train and having a common referencepoint, said gun, director and said point being located in the samesubstantially horizontal deck plane of the ship, and having a target, incombination, means for obtaining a signal proportional to the quantitywhich is the cosine function of the angle of elevation of the targetabove the plane viewed from the director, cos E'b, a potentiometeroperatively connected to said means and adapted to have said cos E'bsignal applied therea-cross, said potentiometer be ing adapted to havethe arm thereof positioned by means corresponding to the parallax angle,Ph, which is the vertical projection in the horizontal plane of theangle subtended at the target by the gun and the director, saidpotentiometer being adapted to supply an output signal corresponding tothe quantity which is the product of the parallax angle and the cosinefunction of the angle of elevation divided by an empirical constant,

Ph cos Eb when positioned by said last named means, means for obtaininga signal corresponding to the quantity which is the sine function of theangle of train, that is, the angle subtended at the director by the gunand the perpendicular projection of said target in the horizontal plane,cor rected for parallax, sin B'rp, an additional potentiometer adaptedto have said sin B'r'p, signal applied thereto, means for positioningthe arm of said last named potentiometer by a signal proportional to therange, R, of the target, to provide an output voltage corresponding tothe quantity which is the sine function of the angle of train correctedby parallax divided by the range,

sin B'r'p a secant attenuator means including a resistance element andincluding an adjustable tap for taking otf a fractional portion of thevoltage thereon and having said sin B'r'p and said Ph cos E'b signalsapplied respectively at each end of said resistance element, saidattenuator means providing an output signal between the tap and one endof the resistance ele ment proportional to the quantity which is theerror signal for the parallax angle, ePh, and means responsive to saidePh signal for positioning the arm of the first named potentiometer bythe parallax angle, Ph.

5. A horizontal parallax angle computation device for determining theangle in the horizontal plane subtended by the displacement of a firstand second point in the horizontal plane at a third point in thehorizontal plane being the vertical projection of a target point not inthe horizontal plane, comprising, a first means producing a voltageproportional to the vertical angle between a line joining said first andtarget point and said plane, a second means producing a voltageproportional to the horizontal angle between said line joining saidfirst and third points, and a line joining said first and second points,a third means for modifying the output of said second means to produce avoltage proportional to the sum of the horizontal angle and the computedparallax angle, a fourth means producing a signal proportional to thesine function of the output of said third means, a fifth outputproducing means which divides the output of said {with means by thedistance between said first and tar get points, a sixth means producinga voltage proportional to the cosine function of the output of saidfirst means, a seventh means combining the output of said sixth meansand the computed parallax angle to produce an output proportional to theproduct of said parallax angle and said output of the said sixth means,an eighth means receiving the outputs of said first, fifth and seventhmeans to produce an error voltage proportional to the product of thedifference between the outputs of said fifth 1 2,575,956

and seventh means and the cosine of the vertical angle, and a ninthmeans receiving the output of said eighth means to produce an outputconnected to said third means and which represents said parallax angle.

References Cited in the file of this patent UNITED STATES PATENTS AginsMar. 29, 1949 Hereford et al. Nov. 20, 1951

